CO2 detectors are used to detect dangerous levels of CO2 in breweries, laboratories and cellars. CO2 levels of 1.5% can already cause hyperventilation and headaches. 10% CO2 levels can lead to death.
Gas detectors detect leakages of flammable gas such as piped Natural Gas or bottled gas (LPG gas). These gas alarms will notify you if for example a cooker hob has been left turned on without a flame or if the gas oven flame has blown out.